At the present time, physicians often treat patients with atrial fibrillation (AF) using radio frequency (RF) catheter systems to ablate conducting tissue in the wall of the Left Atrium of the heart around the ostium of the pulmonary veins. Similar technology, using radiofrequency energy, has been used inside the renal arteries to ablate sympathetic and other nerve fibers that run in the wall of the aorta on the outside of the renal arteries, in order to treat high blood pressure. In both cases these are elaborate and expensive catheter systems that can cause thermal, cryoablative, or other injury to surrounding tissue. Many of these systems also require significant capital outlays for the reusable equipment that lies outside of the body, including RF generation systems and the fluid handling systems for cryoablative catheters.
Because of the similarities of anatomy, for the purposes of this disclosure, the term target vessel will refer here to either the pulmonary vein for AF ablation applications or the renal artery for hypertension therapy applications. The term ostial wall will refer to the wall of the Left Atrium surrounding a pulmonary vein for AF application and to the wall of the aorta for the hypertension application.
In the case of atrial fibrillation ablation, the ablation of tissue surrounding multiple pulmonary veins can be technically challenging and very time consuming. This is particularly so if one uses RF catheters that can only ablate one focus at a time. There is also a failure rate using these types of catheters for atrial fibrillation ablation. The failures of the current approaches are related to the challenges in creating reproducible circumferential ablation of tissue around the ostium (peri-ostial) of a pulmonary vein.
There are also potential risks using the current technologies for RF ablation to create sympathetic nerve denervation inside the renal artery for the treatment of hypertension. The long-term sequelae of applying RF energy inside the renal artery itself are unknown, but this could lead to late restenosis, embolization of debris into the renal parenchyma, or other problems inside the renal artery. There may also be uneven or incomplete sympathetic nerve ablation, particularly if there are anatomic abnormalities, or atherosclerotic or fibrotic disease inside the renal artery, such that there is nonhomogeneous delivery of RF energy. This could lead to treatment failures, or the need for additional and dangerous levels of RF energy to ablate the nerves that run along the adventitial plane of the renal artery. There are also significant safety issues with current technologies related to very long fluoroscopy and procedure times that lead to high levels of radiation exposure to both the patient and the operator, and may increase stroke risk in atrial fibrillation ablation.
Finally, while injection of ethanol as an ablative substance is used within the heart and other parts of the body, there has been no development of an ethanol injection system specifically designed for circular ablation of the ostial wall of a target vessel.